1. Field of the Invention
This invention relates to a treatment composition, system, and method for treating water systems for scale, biofilm and microbial growth, and corrosion. This invention is particularly useful in anthropogenic cooling and chilled water applications, such as cooling towers, and in drain systems, such as floor drains, hospital drains and waterless urinals, and for treating reverse osmosis membrane systems.
2. Description of Related Art
Anthropogenic water systems are critical components commonly found in most of the world's energy producing facilities, industrial and manufacturing plants, hospitals, and other institutional complexes and buildings. These systems consume around 700 billion gallons of water annually with a cost of $1.8 billion in sewage handling costs alone. All of these anthropogenic water systems require some form of treatment, either chemical or non-chemical, to control the build-up of scale, biofilm and other corrosion by-products on the important heat transfer surfaces that are necessary for efficient system operation.
For water systems involving heat exchange, such as cooling towers, effective treatment to remove these contaminants and to prolong the amount of time before the systems are re-contaminated can safe significant amounts of money. An effective and thorough treatment may save costs for labor and treatment chemicals by reducing the frequency of periodic treatments or reducing the amount of chemicals needed for routine maintenance and/or periodic treatments. Such a treatment may also save on energy costs through the operation of clean heat exchange surfaces. Fouling of heat exchange surfaces costs U.S. industry hundreds of millions of dollars every year and is directly related to an increase in energy consumption of almost 3 quadrillion Btus (quads) annually.
To maximize the water usage and minimize waste, many of these systems employ a series of chemical treatments that protect the system against scaling, biofilm formation, and corrosion. For example the Chem-Aqua 15000 MTP product is one of the most common cooling tower chemical treatments, containing 2-phosphonobutane-1,2,4-tricarboxylic acid, and a series of high performance polymers to prevent calcium carbonate scale formation, azoles to inhibit copper corrosion and small amounts of molybdate for trace analysis. Chemical treatments such as the Chem-Aqua 15000 MTP product may be used with a number of non-oxidizing biocides including Bacticide 45 which is a 45% gluteraldehyde solution, Coolicide which is a 15% poly-quaternary ammonium solution, or a 1.5% Isothiazolin solution. In the larger industrial cooling tower systems and the cooling towers for coal and nuclear facilities it is more common to use sodium hypochlorite, 40% sodium bromide, or 11% bromine chloride liquid as the disinfectants.
These chemical treatments allow the water to be reused and recycled a number of times before it becomes necessary to discharge the water and replace it with fresh water. Increasing the duration for which the water may be circulated significantly reduces the amount of water that is discharged to the sewage system and minimizes the amount of make-up water that is needed to replace the bleed off. The chemical treatments also maintain the efficiency of the cooling tower and heat exchanger system. Many prior art treatment compositions and methods involve the use of liquid chemicals, typically shipped in large drums, which may make shipping and handling of the chemical compositions more difficult and expensive. Additionally, many prior art treatment compositions and methods may damage the components of the water system being treated as the chemicals used are highly corrosive. There is also an environmental down side to the treatments. It is estimated that there are 536 billion pounds of water treatment chemicals discharged as a result of cooling tower treatments every year, which may impact a variety of species living in or near areas and water-ways receiving the discharge. Therefore it is desirable to use treatment chemicals that are considered less toxic. For example, citric acid and sodium citrate, which are both approved food additives, have been used in treatment compositions.
Many prior art treatment compositions and methods are also effective at removing biofilms or require the use of strongly acidic, oxidizing, and toxic biocides for removal. Biofilms contain mixed communities of bacteria including various species embedded in an exopolymer or “slime layer”. As bacteria begin to attach to a surface, they secrete polymers, such as polysaccharides and glycoproteins called fibronectin. These allow the bacteria to adhere to a surface and form the conditioning layer of the biofilm. Once a confluent surface of sessile cells has formed, any other bacteria that contact this layer will be captured. Thus bound in this way, these bacterial cells begin to produce anchoring organelles and other compounds, allowing a secondary layer to form on top of the conditioning layer. As cells continue to attach and accumulate, underlying layers continue to reproduce and create a dense bacterial cluster. As these biofilm layers form they also accumulate other inorganic and organic debris that grow within the pipe restricting flow and causing blockages.
Similar issues, particularly with biofilms, are also encountered in drainage systems, such as hospital drains, industrial wastewater drains, and waterless urinals. During normal use, drains and drainage systems transport liquids such as water, urine, or processing fluids to treatment or discharge facilities. Even though some of these liquids are sterile when then enter the drain systems, it is virtually impossible to keep all fluids sterile when they enter the outside environment. As they flow through the drainage system they accumulate naturally occurring micro flora and other heterotrophic microorganisms that, over time, result in the formation of biofilms along the surfaces of the walls of the pipes. In hospitals, especially dialysis centers, this could present a direct risk of infection to patients. Biofilms may also grow rapidly and result in clogged drains and piping in drainage systems.
Products and services for the cleaning and remediation of drains and drainage systems worldwide is estimated to exceed $2 billion annually, most of which is driven by labor costs that consume $0.87 for every dollar spent. As with the chemicals used to clean cooling tower and similar industrial water systems, the prior art drain remediation and cleaning technologies use aggressive chemicals, including concentrated acidic or basic compounds. These compounds need special handling and have to be stored on site or require specialty power cleaners such as water jets or drum and sectional machines that require experienced operators. They also typically involve added costs for protective gear for operators handling the chemicals and added training cots.
Many of the chemical drain cleaning products are sold in solid or liquid forms and are classified as alkaline drain openers, acid drain openers, or enzymatic drain cleaners. Alkaline drain openers come as either a solid or liquid and typically contain sodium or potassium hydroxide as well as sodium hypochlorite. In some cases the alkaline drain openers are sold as two part mixtures that will form a foam when mixed together in the drain. Alkaline drain openers can dissolve proteins and fats within the drain through an alkaline hydrolysis of the amide or ester. Acid drain openers usually contain a strong acid such as sulfuric acid that dissolves fats and proteins via an acid hydrolysis mechanism. They also have dehydrating properties that help them dissolve paper. Unlike the alkaline drain openers, most of these acid cleaners must be applied by a licensed operator. Enzymatic drain cleaners use bacterial cultures and concentrated enzymes that react with organic residues on the walls of the pipes, dissolving it to keep the drain flowing. These drain cleaners are intended to be used as a general maintenance treatments and not to remove clogs or blockages that have already formed. Mechanical drain cleaners are also known in the prior art and involve a number of mechanical and physical techniques to unclog and clean drain systems, which may be used alone or in combination with chemical cleaners. These mechanical cleaners include auger systems, air burst systems, plumber snakes, and water jet systems. These mechanical systems are advantageous because they do not have the hazards associated with the storage and use of harsh chemicals and they are relatively inexpensive and readily available for rent in most hardware stores. However, the disadvantage is that the mechanical removal of clogs and other biological deposits with these methods can be expelled into the environment putting the operator and other people in the vicinity at risk of exposure to biological pathogens. This is of particular concern in hospitals and dialysis centers where immunocompromised patients are being treated.
Biofilm growth or biofouling is also a major issue in reverse osmosis systems, such as desalination plants. Reverse osmosis is a type of water treatment process that removes inorganics and organics from solution. These systems use a semi-permeable membrane to allow water to flow through the membrane by applying high pressure to overcome osmotic pressure. Reverse osmosis systems vary in size depending on application, and can treat multiple types of water such as brackish and sea water. Reverse osmosis systems also include pre-treatments (chemical feed, coagulation/flocculation/sedimentation, sand filtration, microfiltration (MF), and ultrafiltration (UF)) and post-treatments (UV disinfection). Biofouling in a reverse osmosis system increases energy consumption in order to maintain the system's feed pressure, reduces permeate flux, and increases the amount of chemical feed needed to clean the membrane. With increased chemical feed, the lifespan of the membrane will decrease due to the degradation of the membrane, which allows more solids to pass through the membrane which would require more post-treatment of the permeate flux. Prior art biological control products, such as alkaline cleaners or non-oxidizers, have been used to reduce or prevent the formation of biofilm. However, these products are either too corrosive and could destroy the integrity of the membrane, or highly toxic. Depending on their size, membranes cost from around $258.00 to $767.00, making it important to prolong the life of the membrane as much as possible. With prior art treatments, the average lifespan of a reverse osmosis spiral-wound membrane is 3 years